Patch:Slippery tiles
Slippery tiles are tiles in Keen Vorticons that make Keen slip along them, losing some control. Keen cannot stop walking on them once he starts, though he can change speed and direction. Keen can only stand still if he lands perfectly vertically on them. They are only found by default in Keen 1, but are possible in all Keen Vorticons episodes.
The 'slippery tile' is actually a tile property of the top of the tile. Tops of tiles can have four values, nothing, solid, slippery and ice. In this case the slippery value is $02. The 'ice' value has a far, far more complex behavior and is discussed under Patch:Ice tiles.
Slippery tile check
By default only 'normal' tiles cause Keen to slow down and stop walking when he walks across them without pressing any arrow keys. This means that both ice and slippery type tiles will not alter Keen's speed. However ice type tiles limit Keen's movement, speed and control in a number of other ways whereas slippery tiles merely prevent Keen from stopping walking, and indirectly at that. This check is for the normal tile type, type $01.
Slippery tile checks
#Tile check to slow Keen's walking - Keen 1
%patch $395B [$01] {$75}
#Tile check to slow Keen's walking - Keen 2
%patch $679D [$01] {$75}
#Tile check to slow Keen's walking - Keen 3
%patch $6FFD [$01] {$75}